Spark gap device



p 1957 J. H. SNELL, JR 2,805,355

SPARK GAP DEVICE Filed Sept. 1,-1953 x M Y I j 7 "-1 I6 Jqme g sgell, Jr.

by if R 7% i Hi5 fl/fomgy.

United States Patent Ofiice Patented Sept. 3, 1957 SPARK GAP DEVICE James H. Snell, Jr., Pittsfield, Mass., assignor to General Electric Company, a corporation of New York Application September 1, 1953, Serial No. 377,831

3 Claims. (Cl. 313-308) This invention relates to a spark gap device, and more particularly, to a spark gap device having preionizing means.

Preionizing means for spark gap devices are wed known in the prior art and are used in spark gap devices to insure breakdown of the spark gap at a low and consistent voltage. As far as I am aware, all the prior preionizing means are directly connected to one or both of the main gap electrodes. In such an arrangement it is often diflicult to avoid objectionable radio noises or interference at or below the rated voltage of the spark gap device. I have discovered that if the preionizing means is not directly connected to either or both of the main gap electrodes but capacitively coupled to both of the main electrodes radio noise or interference is reduced.

Accordingly, it is an object of this invention to provide in a spark gap device comprising two spaced electrodes defining a spark gap therebetween, and a preionizing element which is capacitively coupled to said electrodes.

My invention comprises an electrical circuit having two spaced electrodes therein defining a spark gap therebetween and a preionizing element solely capacitively coupled to said electrodes.

The invention will be better understood by considering the following description taken in connection with the accompanying drawing and its scope will be pointed out in the appended claims.

In the drawing Fig. 1 is a perspective illustration, partly in section, of an embodiment of my invention. Fig. 2 is a perspective disassembled view of the spark gap device shown in Fig. 1. Fig. 3 is a sectional side view of the spark gap device shown in Fig. 1 to better illustrate the spark gap arc chute.

Referring now to the drawing, and more particularly to Fig. 1, shown therein is a spark gap device comprising two superposed insulating material disks or blocks and 11. Insulating material blocks 10 and 11 are nested with respect to each other to define a shallow circular-like arc chute or chamber 12. Within said arc chute are two main arcing electrodes 13 and 14. Arcing electrodes 13 and 14 are spaced with respect to each other to define a spark gap 15 therebetween. Positioned on the upper surface of insulating material block 10 is a contact plate 16. Positioned adjacent the bottom surface of the lower insulating material block 11 is a contact plate 17. Electrode 13 is connected to insulating material block 10 by a pin or the like which extends through said insulating block 10 and is electrically connected to contact plate 16. Main arcing electrode 14 is likewise connected by a pin to the contact plate 17 to be placed in electrical contact therewith.

The spark gap device just described can be used to protect a transmission line 18 or other electrical apparatus from lightning surges or the like. Thus an electrical coil 19 surrounds the spark gap device and one end 20 of said electrical coil 19 is connected to transmission line 18 and the other end 21 of coil 19 is connected to the contact plate 16. A protective gap 22 shunts the electrical coil 19 to protect the electrical coil 19 during the lightning surge. The contact plate 17 is connected to ground and if so desired a valve type element 23 can be interposed between the contact plate 17 and ground to limit the current through the spark gap device.

When lightning strikes transmission line 18 the current resulting from the lightning will cause gap 22 to spark over whereby the coil 19 will be shunted. Most of the current due to the lightning surge will pass from transmission line 18 across gap 22 to contact plate 16 and thence to main arcing electrode 13. The gap 15 between electrodes 14 and 13 will break down whereby the lightning surge will pass to ground. After the lightning surge has been dissipated, the power follow current from transmission line 18 will tend to maintain the arc across main arcing electrodes 13 and 14. Subsequent to the passage of the lightning surge to ground the arc across protective gap 22 will gradually cease. However, the power follow current from line 18 will flow through line 20 and coil 19 to line 21 and thence to contact plate 16 and main arcing electrode 13. Since the spark gap 15 was initially broken down by the lightning surge the power foliow current will pass from electrode 13 to electrode 14 and thence to ground. The How of said power follow current through coil 19 will produce a magnetic field which will be substantially perpendicular to the insulating ma terial blocks 10 and 11. Said magnetic field will react with the magnetic field of the arc across main spark gap 15 whereby the arc across main arcing electrodes 13 and 14 will be forced to move away from the electrodes 13 and 14 towards the remote side 24 of arc chute 12. Accordingly, the arc is elongated and is cooled when it comes into contact with the inner surfaces of the insulating rnaterial blocks 10 and 11 defining 'arc chute 12. As is well known in the prior art, when the power follow current reaches current zero the arc across gap 15 will be interrupted.

Valve element 23 can be a non-linear resistor of the type which has the characteristics of presenting a low resistance when subjected to a high voltage and presenting a high resistance when subjected to a low voltage. Accordingly, valve element 23 will offer very little re sistance to the high voltage lightning surge thereby permitting easy passage of the lightning surge to ground. However, the valve element 23 will present a high resistance to the comparatively low voltage power follow current thereby tending to limit said current.

As hereinfore stated it is well known in the prior art to incorporate a preionizing means into a spark gap device to insure a low and consistent sparkover or breakdown voltage. However, as far as I am aware, all the prior preionizing means are directly electrically connected to one or both of the main arcing electrodes. Such an arrangement often produces undesirable radio interference or noise.

In my invention the preionizing means is only capacitively coupled to the main arcing electrodes in a wireless non-inductive resistanceless manner whereby objectionable radio interference or noise is substantially reduced. The preionizing means comprises a preionizing element or electrode 25. As seen most clearly in Fig. 3, one end of the electrode 25 bears against the bottom surface of the insulating material block 10. The other end of the preionizing electrode or element 25 is connected to a generally Z-shaped spring element 26 which enters a slot 27 in block 11 whereby said other end of electrode 25 is in contact with insulating material block 11. The preionizing element 25 is positioned closely adjacent to but not within the spark gap 15 and is sandwiched in between the insulating material blocks 10 and 11 as seen most clearly in Fig. 3 whereby the element 25 is structurally connected to the electrodes 13 and 14 solely by electrical insulating material. Preferably the electrode 25 is positioned adjacent the side of arc chute 1 .2 opposite to side 24 so that the electrode 25 does not lie in the path of elongation of the arc across spark gap 15. Aiso, electrode 25 is positioned along a line substantially midway of and perpendicular to spark gap 15 for balanced capacitive coupling with electrodes 33 and 14. The distance between electrode 25 and spark gap 15 is adjusted so that an arc will not occur between electrodes 13 and 14 and electrode 25. However, electrode 25 is laced and 14 solely by integral portions of insulating material blocks 10 and 11. Accordingly, my preionizing element or electrode 25, is only capacitively coupled to the main arcing electrodes 13 and 14. The end of preionizing electrode 25 which contacts the bottom surface of insulating material block 10 emits corona thereby preionizing 1 the space or gap 15 between arcing electrodes 13 and 14 whereby a low and consistent sparkover voltage is insured with substantially no radio noise or interference at or below the rated voltage of the spark gap device. contact with the lower surface of insulating material block 10 is suitably rounded oil or dome-shaped so that it makes point contact with said lower surface. However, said point contact is not sharp enough to cause the emission of corona and production of radio noise or interference below rated voltage.

While these has been shown and described a particular embodiment of the invention, it will be obvious to those skilled in the art that changes and modifications may be made without departing from the invention, and that it is intended by the appended claims to cover all such changes and modifications as fall within the true spirit and scope of the invention.

What I claim as new and desire to secure by Letters Patent of the United States is:

1. A spark gap device comprising two insulating material blocks superposed with respect to each other and defining an arcing chamber therebetween, two main spaced electrodes positioned within said chamber and defining a spark gap therebetween, one of said electrodes attached to one of said blocks and the other of said electrodes attached to the other of said blocks, and a preionizing electrode for said spark gap which is solely capacitively coupled with said main electrodes in a wireless, non- The upper end of electrode 25 which makes said main electrodes solely by integral portions of said blocks.

2. In a spark gap device comprising an electrical circuit having two spaced main electrodes therein defining a spark gap therebetween, two superposed insulating material blocks defining an arcing chamber therebetween, said electrodes positioned within said chamber, one of said electrodes connected to one of said blocks and the other of said electrodes connected to the other of said blocks, and a preionizing electrode for said spark gap which is solely capacitively coupled to said-main electrodes in a wireless, non-inductive and-resistanceless manner, said preionizing electrode positioned adjacent but not within said spark gap and spaced from said main electrodes, said preionizing electrode mounted adjacent one of its ends in said one block and abutting at its other end said other block.

3. A spark gap device comprising two superposed insulatin material blocks defining a shallow arc chute therebetween, two main spaced electrodes positioned within said are chute and defining a spark gap therebetween, means for moving an arc ignited between said main electrodes towards a remote side of said are chute whereby said are is elongated, a preionizing electrode positioned adjacent but not within said spark gap, said preionizing electrode spaced from said main electrodes and spark gap and positioned adjacent a side of said are chute which is opposite to said remote side, said electrode positioned along a line extending substantially perpendicular to said spark gap midway of said spark gap, one end of said preionizing electrode mounted in one of said blocks and the other end of said preionizing electrode contacting a surface of said are chute whereby said preionizing electrode is solely equally capacitively coupled to said main electrodes in a wireless, non-inductive and resistanceless manner, said contacting end being dome-shaped and making point contact with said surface.

References Cited in the file of this patent UNITED STATES PATENTS 551,786 Potter Dec. 24, 1895 1,477,308 Brackett Dec. 11, 1923 1,562,959 Harrington Nov. 24, 1925 2,644,116 Olsen June 30, 1953 2,727,187 Webb et al Dec. 13, 1955 

